The invention relates to a seal arrangement for a piston rod, particularly for a shock absorber of a motor vehicle wherein the piston rod is arranged in a cylinder so as to be axially movable therein and at least two seal elements are provided between the piston rod and the inner wall of the cylinder.
Such an arrangement is known, for example, from EP-A 00 32 988. The seal arrangement shown in this publication comprises a first seal ring in the form of a sleeve which includes a sealing lip in contact with the outer surface of the piston rod. A part of the sleeve extends around a second seal ring which is axially spaced from the first seal ring and is also in contact with the piston rod.
This arrangement has a disadvantage in that the first seal ring has an irregular cross-sectional shape and its manufacture is therefore relatively expensive. Because of the irregular shape, also the tensions in the seal ring material are not uniform; there is the danger of rupture in areas which are subjected to high tensions. Also, it is not insured that the pressure required for an effective seal is always present at the seal lip over a long period of operation.
It is furthermore disadvantageous that the second seal ring, although improving the sealing effect, increases the friction at the surface of the piston rod so that a greater force is required for moving the piston rod. Because of the greater force required for moving the piston, the material wear is also increased.
It is the object of the present invention to provide with simple means a seal arrangement which has little wear and operates reliably.